Mystery No-Start

C

c4 Travis

Member
I pulled out my fuel pump sending unit to replace the gasket on it (I had previously replaced the fuel pump without putting in a new gasket). I was careful and meticulous in removing and replacing, however, when I put everything back together the vehicle would not run.

It would turn over and run for a moment and then die. My fuel pump is running and I have pressure at the rail. I've checked all of the fuses, and I know the fuel pump is running. I even switched to a different (known good) fuel pump. This car will not run for more than a moment before falling on its face.

The only code it's flashing is 34 (low voltage on MAF at cruise speed). Is this related? Would removing my fuel pump sending unit effect my MAF (obviously not but hey, I'm open to ideas no matter how crazy.)

This one is perplexing me, any ideas?!

Trav
 
I've encountered that problem in the past. I have this switch jumped while I'm troubleshooting. The car is running for a moment and then dying. Anything else? I'm at a complete loss what happened here.
 
Open the Hood & Wiggle the HEI POWER LEAD.
Its the big fat 1/4" inch Pink /Red wire.
See if your C4 Will start & stay running.
 
c4 Travis said:
I've encountered that problem in the past. I have this switch jumped while I'm troubleshooting. The car is running for a moment and then dying. Anything else? I'm at a complete loss what happened here.
Click to expand...
read thru the link and sub links, I posted.
a logical step by step ,isolate and test process will locate the cause,
first step is to use a NOID light and VERIFY spark at the plugs to determine if its the injectors or the ignition that caused the engine to stall
look its a simple test and isolate process, that most guys get intimidated by simply because they don,t read the linked info and do the suggested tests in the sub links, it always comes down to the basics of COMPRESSION, FUEL FLOW,AIR FLOW,VACUUM LEAKS ,MISSING OR DEFECTIVE SENSOR READINGS,LOOSE ELECTRICAL CONNECTIONS,BLOWN FUSES LACK OF FUEL PRESSURE, AND LACK of CORRECTLY TIMED IGNITION SPARK., so you isolate and test

viewtopic.php?f=50&t=9478&p=34812&hilit=noid#p34812

viewtopic.php?f=32&t=1401

viewtopic.php?f=70&t=7309&p=24862&hilit=noid+test+light#p24862

viewtopic.php?f=55&t=606&p=7969&hilit=noid#p7969

viewtopic.php?f=70&t=9450&p=34592&hilit=sensors#p34592

viewtopic.php?f=55&t=1241

viewtopic.php?f=80&t=728

viewtopic.php?f=32&t=596
 
c4 Travis said:
I'll start by purchasing a fuel pressure gauge. You have this one listed in one of your posts. I almost purchased but it says it does not work on GM throttle body systems. I doubt you would list one that doesn't work on a corvette though. Is this gauge good for my vehicle?

http://www.harborfreight.com/fuel-injec ... 92699.html
Click to expand...

it works ok, you just need to figure out how to tap into the fuel rail or line and that varies between years but certainly not a difficult issue to either remove a shrader valve and insert an adapter barb fitting or splice a TEE into a fuel line as a temp. test point, certainly any mechanic has an assortment of the common barb fittings required in a test kit

bbtee1.jpg

bbtee2.jpg
 
I purchased that exact gauge that you recommended and tested at the fuel rail. I only got 10 psi so I tested in the back as well, right at the sending unit. I also go 10 psi there. I installed another fuel pump I had lying around and still only got 10 psi. On the off chance that I had two bad fuel pumps, I threw a new fuel pump in there and still got 10 psi rather than the 38-40 that I need. The car starts and falls flat on it's face. I have 12volts and the fuel pump connector, why am I only getting 10 psi?
 
You have a defective fuel pressure regulator. Likely.
Can service replace by removing upper TPI Plenum.
 
I just replaced the fuel pressure regulator though. Doesn't the car have to be running for the vacuum to work on the regulator? I only have 10psi when I put the gauge in line with the fuel pump sending unit outlet.
 
You have to remove the gas door on your C4 Corvette again.
With Vice Grip pliers pinch off the Fuel Return Hose.
Do you have at least 43.5psi now ?
Should reach to 90-110psi if the fuel pump is healthy & new.

Brian
 
SOLUTION!!

Thanks for all of the info guys!

Ultimately, I inspected the entire sending unit because why would 3 known good fuel pumps read 10psi directly at the sending unit??? This is what I found: On the fuel out and return lines for the sending unit (inside tank, directly after fuel pump) there were two identical holes adjacent to each other (one on either line). It occurred to me that there was a support bracket here that bound the two lines together. I must have knocked it off during my initial removal when I tried to put my gasket in there in the first place. On the fuel out line, I added some rubber hose and clamps. My fuel pressure went up to 38 and the car started and ran very fast through my neighborhood.

I hope my experience helps anyone who has a similar problem.

Travis
 

My fuel pressure went up to 38 and the car started and ran very fast through my neighborhood.
Click to expand...

Well I hope you got it back in the driveway and engine off before the cops showed up! :lol:

Glad you found your problem, sometimes we are own worst enemies.

 
Thanks rick! I was definitely my own worst enemy on this one. It's not the first time and it definitely won't be the last time!!
 
c4 Travis
could you explain what you found and what you did to correct the problem in more detail, some of what I think your saying has me a bit confused
 
The last time around Fuel Pump repair , C4 Travis used worm gear hose clamps on that short section of 5/16" ID. rubber fuel line hose Grumpy.
 
I wish now that I had taken pictures but I was too excited about having solved the problem.

The two metal lines that are part of the actual sending unit had an apparent small bracket that ran across them. When I removed the sending unit, I must have knocked off the little support bracket. This left two little perfectly round 1/8 inch holes in the lines. This is why I had no pressure from 3 different fuel pumps. The pressure was dropping off at the hole in the sending unit before it ever left the tank.

REPAIR: I took a piece of fuel rated rubber hose and sliced one side so I could fit it over the feed line to cover the hole. I put a clamp directly over the hole on the rubber hose and one more on either side. Surely overkill but, hey I don't want to do it again. Then I finally installed my new home made gasket and we were off to the races.

I hope that makes more sense. If for some reason I have to open it up again, I will post pictures.
 
ap010.jpg

PLEASE! don,t think this is CRITICIZING ,ANYONE OR ANY THING! I 100% only mean this to be an opportunity to aid to readers of this thread in the future to add to their skills and understanding of testing and how to arrive at a solution quickly :mrgreen:
I,ll post a picture here that might help those reading thru the thread who have little experience with c4 corvette fuel pumps, and I can,t help but think the links poster earlier were not carefully read thru,YES I ALSO SKIPPED READING LINKS YEARS AGO, now I try to read all I can!
and let me point out IM very happy you took the time to post what you found for a solution and that you solved it!
grumpyvette said:
.........
viewtopic.php?f=32&t=1401

http://members.shaw.ca/corvette86/Engin ... ontRun.pdf

http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf
Click to expand...

leakfuell.png


the chart in the last link points to the issue, and yes I ignored links and shop manuals when I was younger but with age and frustration came the realization that stopping to read usually provided CORRECT answers far faster than random guesses made by ME and MY FRIENDS, as SOMEONE ELSE had designed and built and written the instructions, someone who knew what to look for( G.M. design engineers) simply because THEY designed and BUILT it and had decades of experience. so I eventually learned to stop guessing and start reading and a whole new concept dawned, IN MY SKILL SET!......research and testing, ..since then things have become different but easier for me!, and yes I still make mistakes, and yes I still have freinds who don,t understand why I insist on grabbing a shop manual, fuel pressure gauge and multi meter almost every time they mention a no start issue on a corvette, before i even lift the cars hood.
look I know how frustrating tracking down a problem on a car can be! that's one of the main reasons I started the site! to make it easier for guys who were members to AVOID the HOURS of FRUSTRATION I regularly went thru in my early years because I did not have a mechanic/engineer and mentor on tap every time I ran into problems, who was willing to teach me all the tricks and answer questions
 
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